Method calculateLabelRotation

src/core/core.scale.js:586–623

()

    call(this.options.beforeCalculateLabelRotation, [this]);
  }
  calculateLabelRotation() {
    const options = this.options;
    const tickOpts = options.ticks;
    const numTicks = getTicksLimit(this.ticks.length, options.ticks.maxTicksLimit);
    const minRotation = tickOpts.minRotation || 0;
    const maxRotation = tickOpts.maxRotation;
    let labelRotation = minRotation;
    let tickWidth, maxHeight, maxLabelDiagonal;

    if (!this._isVisible() || !tickOpts.display || minRotation >= maxRotation || numTicks <= 1 || !this.isHorizontal()) {
      this.labelRotation = minRotation;
      return;
    }

    const labelSizes = this._getLabelSizes();
    const maxLabelWidth = labelSizes.widest.width;
    const maxLabelHeight = labelSizes.highest.height;

    // Estimate the width of each grid based on the canvas width, the maximum
    // label width and the number of tick intervals
    const maxWidth = _limitValue(this.chart.width - maxLabelWidth, 0, this.maxWidth);
    tickWidth = options.offset ? this.maxWidth / numTicks : maxWidth / (numTicks - 1);

    // Allow 3 pixels x2 padding either side for label readability
    if (maxLabelWidth + 6 > tickWidth) {
      tickWidth = maxWidth / (numTicks - (options.offset ? 0.5 : 1));
      maxHeight = this.maxHeight - getTickMarkLength(options.grid)
				- tickOpts.padding - getTitleHeight(options.title, this.chart.options.font);
      maxLabelDiagonal = Math.sqrt(maxLabelWidth * maxLabelWidth + maxLabelHeight * maxLabelHeight);
      labelRotation = toDegrees(Math.min(
        Math.asin(_limitValue((labelSizes.highest.height + 6) / tickWidth, -1, 1)),
        Math.asin(_limitValue(maxHeight / maxLabelDiagonal, -1, 1)) - Math.asin(_limitValue(maxLabelHeight / maxLabelDiagonal, -1, 1))
      ));
      labelRotation = Math.max(minRotation, Math.min(maxRotation, labelRotation));
    }

    this.labelRotation = labelRotation;
  }
  afterCalculateLabelRotation() {
    call(this.options.afterCalculateLabelRotation, [this]);
  }